Heat source unit and freezer

Abstract

To stably start low-stage compression units and a high-stage compression unit.SOLUTION: A controller (130) executes: a first operation of reducing a high pressure of a refrigerant circuit (6) or a suction pressure of a high-stage compression unit (23); a second operation of starting the high-stage compression unit (23) after the first operation; a third operation of suctioning a refrigerant into the high-stage compression unit (23) through bypass flow paths (56, 57) after the second operation; and a fourth operation of starting low-stage compression units (21, 22) after the third operation.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present disclosure relates to a heat source unit and a refrigeration device. [Background technology]

[0002] The refrigeration device described in Patent Document 1 includes a refrigerant circuit having a low-stage compression section and a high-stage compression section. The refrigerant circuit performs a refrigeration cycle in which the refrigerant compressed in the low-stage compression section is further compressed in the high-stage compression section. The refrigerant circuit of Patent Document 1 also performs a refrigeration cycle in which the refrigerant is compressed to a critical pressure or higher. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-184231 A Summary of the Invention [Problem to be solved by the invention]

[0004] The refrigeration system described in Patent Document 1 performs a refrigeration cycle that compresses the refrigerant to above the critical pressure, and therefore the high-pressure in the refrigerant circuit is higher than in a refrigeration system that performs a subcritical refrigeration cycle. Therefore, if the low-stage compression section and the high-stage compression section are simply started, depending on the operating conditions, the high-pressure becomes excessively high, and the low-stage compression section and the high-stage compression section cannot be started stably.

[0005] An object of the present disclosure is to stably start up a low stage compression section and a high stage compression section. [Means for solving the problem]

[0006] The first aspect is directed to a heat source unit applied to a refrigeration system (1) having a refrigerant circuit (6) performing a refrigeration cycle in which a refrigerant is compressed to a critical pressure or higher. The heat source unit (10) includes low-stage compression sections (21, 22), a high-stage compression section (23) that compresses the refrigerant compressed in the low-stage compression sections (21, 22), a heat-source-side heat exchanger (24), bypass flow paths (56, 57) that communicate between the suction sides and discharge sides of the low-stage compression sections (21, 22), and a control device (130). The control device (130) executes a first operation of reducing the high pressure of the refrigerant circuit (6) or the suction pressure of the high-stage compression section (23), a second operation of starting up the high-stage compression section (23) after the first operation, a third operation of sucking refrigerant into the high-stage compression section (23) through the bypass flow paths (56, 57) after the second operation, and a fourth operation of starting up the low-stage compression sections (21, 22) after the third operation.

[0007] In the first mode, the first operation reduces the high-pressure pressure of the refrigerant circuit (6) or the suction pressure of the high-stage compression section (23). Therefore, in the second operation after the first operation, even if the high-stage compression section (23) is started, the high-pressure pressure of the refrigerant circuit (6) can be prevented from becoming excessively high. In the third operation after the second operation, the refrigerant is sucked into the high-stage compression section (23) through the bypass flow path (56, 57). Therefore, the pressure on the suction side of the low-stage compression section (21, 22) can be made close to the pressure on the discharge side of the low-stage compression section (21, 22). In the fourth operation after the third operation, the low-stage compression section (21, 22) is started. At this time, the difference (differential pressure) between the pressure on the suction side of the low-stage compression section (21, 22) and the pressure on the discharge side of the high-stage compression section (23) is small, so that the load on the low-stage compression section (21, 22) associated with the differential pressure at the start of the low-stage compression section (21, 22) can be reduced. By the above-mentioned operations, the low stage compression section (21, 22) and the high stage compression section (23) can be started up stably.

[0008] The second aspect is the first aspect, further comprising a liquid side flow path (40) connected to the heat source side heat exchanger (24), a gas-liquid separator (25) provided in the liquid side flow path (40) and separating a refrigerant into a gas refrigerant and a liquid refrigerant, a gas vent flow path (41) connecting the inside of the gas-liquid separator (25) to the suction side of the high-stage compression section (23), and a cooling section (95) for cooling the refrigerant inside the gas-liquid separator (25). In the first operation, the control device (130) causes the gas-liquid separator (25) to cool by the cooling section (95).

[0009] In the second aspect, in the first operation, the cooling section (95) cools the refrigerant inside the gas-liquid separator (25). When the refrigerant inside the gas-liquid separator (25) is cooled, the pressure inside the gas-liquid separator (25) decreases. The suction side of the high-stage compression section (23) communicates with the interior of the gas-liquid separator (25) through the gas vent passage (41). Therefore, the suction pressure of the high-stage compression section (23) can be reduced by the first operation.

[0010] In the third aspect, the cooling system of the first aspect further includes a fan (12) that transports air passing through the heat source side heat exchanger (24). In the first operation, the control device (130) increases the rotation speed of the fan (12).

[0011] In the third aspect, in the first operation, the rotation speed of the fan (12) corresponding to the heat source side heat exchanger (24) is increased, whereby the refrigerant in the heat source side heat exchanger (24) is cooled and the pressure of the refrigerant is reduced, thereby reducing the high pressure of the refrigerant circuit (6).

[0012] The fourth aspect is the first aspect, and further includes a liquid side flow path (40) connected to the heat source side heat exchanger (24), a gas-liquid separator (25) provided in the liquid side flow path (40) and separating a refrigerant into a gas refrigerant and a liquid refrigerant, a gas vent flow path (41) connecting the inside of the gas-liquid separator (25) with the suction side of the high-stage compression section (23), and a first valve (42) provided in the gas vent flow path (41). In the first operation, the control device (130) increases the opening degree of the first valve (42). Here, "increasing the opening degree of the first valve (42)" means both further increasing the opening degree of the first valve (42) in the open state and opening the first valve (42) in the closed state.

[0013] In the fourth aspect, in the first operation, when the opening degree of the first valve (42) increases, the refrigerant in the gas-liquid separator (25) is sucked into the high-stage compression section (23) through the gas vent passage (41). As a result, the internal pressure of the gas-liquid separator (25) decreases. If the pressure of the refrigerant in the heat source side heat exchanger (24) of the refrigerant circuit (6) is high, the refrigerant flows into the gas-liquid separator (25). As a result, the high pressure of the refrigerant circuit (6) can be reduced.

[0014] The fifth aspect is the first aspect, further comprising a communication passage (51) that communicates the discharge side and the suction side of the high-stage compression section (23) with each other, and a second valve (53) provided in the communication passage (51). In the first operation, the control device (130) increases the opening degree of the second valve (53). Here, "increasing the opening degree of the second valve (53)" means both further increasing the opening degree of the second valve (53) that is in an open state and opening the second valve (53) that is in a closed state.

[0015] In the fifth aspect, in the first action, when the opening degree of the second valve (53) increases, the refrigerant on the discharge side of the high-stage compression section (23) returns to the suction side of the high-stage compression section (23) through the communication passage (51). As a result, it is possible to reduce the high-pressure on the discharge side of the high-stage compression section (23), i.e., the high-pressure in the refrigerant circuit (6).

[0016] In a sixth aspect, in any one of the first to fifth aspects, the control device (130) executes the first action before stopping the high-stage compression section (23) or while the high-stage compression section (23) is stopped.

[0017] In the sixth aspect, the high pressure in the refrigerant circuit (6) and the suction pressure of the high stage compression section (23) can be reduced before or during the shutdown of the high stage compression section (23).

[0018] In a seventh aspect, in any one of the first to sixth aspects, the control device (130) executes the second operation after the high pressure in the refrigerant circuit (6) or the suction pressure of the high-stage compression section (23) becomes equal to or lower than a predetermined value.

[0019] In the seventh aspect, the high-stage compression section (23) can be started up under the condition that the high pressure in the refrigerant circuit (6) and the suction pressure of the high-stage compression section (23) decrease.

[0020] An eighth aspect is a refrigeration system including the heat source unit (10) according to any one of the first to seventh aspects.

[0021] A ninth embodiment is the eighth embodiment, wherein the refrigerant is carbon dioxide.

[0022] In the ninth aspect, in a refrigeration system performing a refrigeration cycle using carbon dioxide in which high-pressure is particularly likely to increase, the low-stage compression section (21, 22) and the high-stage compression section (23) can be started up stably. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a piping diagram of a refrigeration device according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing the connection relationship between the controller and its peripheral devices. [Diagram 3] FIG. 3 is a configuration diagram of the flow path switching mechanism. [Figure 4] FIG. 4 is a piping diagram of a refrigeration system, showing the flow of refrigerant during cooling operation. [Diagram 5] FIG. 5 is a piping diagram of a refrigeration system, showing the flow of refrigerant during cooling operation (defrost operation). [Figure 6] FIG. 6 is a piping diagram of a refrigeration system, showing the flow of refrigerant during cooling operation (defrost operation). [Figure 7] FIG. 7 is a piping diagram of a refrigeration system, showing the flow of refrigerant during heating operation. [Figure 8] FIG. 8 is a piping diagram of the refrigeration system, showing the flow of refrigerant in the first heating / cooling operation. [Figure 9] FIG. 9 is a piping diagram of the refrigeration system, showing the flow of refrigerant in the second heating / cooling operation. [Figure 10] FIG. 10 is a piping diagram of the refrigeration system, showing the flow of refrigerant in the third heating / cooling operation. [Figure 11] FIG. 11 is a flow chart of control regarding the start-up of the compression element. [Figure 12] FIG. 12 is a flowchart of control regarding the startup of the compression element in the first modification. [Figure 13] FIG. 13 is a diagram of the second modification corresponding to FIG. [Figure 14] FIG. 14 is a flowchart of control regarding activation of a compression element in the second modification. [Figure 15] FIG. 15 is a flowchart of control regarding activation of a compression element in the third modification. [Figure 16] FIG. 16 is a flowchart of control regarding the start-up of the compression element in the fourth modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible within the scope of the technical idea of ​​the present disclosure. Since each drawing is intended to conceptually explain the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for easy understanding.

[0025] The refrigeration system (1) according to this embodiment is a refrigeration cycle system that performs a refrigeration cycle. The refrigeration system (1) simultaneously cools an object to be cooled and conditions the air inside the room. The object to be cooled here includes the air inside equipment such as a refrigerator, a freezer, and a showcase. Hereinafter, such equipment will be referred to as a refrigeration facility.

[0026] (1) Overall structure As shown in Fig. 1, the refrigeration system (1) includes a heat source unit (10) installed outside a room, an air conditioning unit (60) that conditions the air inside the room, and a cold-setting unit (70) that cools the air inside the room. One air conditioning unit (60) is illustrated in Fig. 1. The refrigeration system (1) may include two or more air conditioning units (60) connected in parallel. One cold-setting unit (70) is illustrated in Fig. 1. The refrigeration system (1) may include two or more cold-setting units (70) connected in parallel.

[0027] The refrigeration system (1) includes four communication pipes (2, 3, 4, 5) that connect the heat source unit (10), the air conditioning unit (60), and the cooling unit (70). In the refrigeration system (1), the heat source unit (10), the air conditioning unit (60), and the cooling unit (70) are connected by these communication pipes (2, 3, 4, 5) to form a refrigerant circuit (6).

[0028] The refrigerant circuit (6) contains a filled refrigerant. The refrigerant circuit (6) circulates the refrigerant to perform a refrigeration cycle. In this embodiment, the refrigerant is carbon dioxide. The refrigerant circuit (6) performs a refrigeration cycle in which the refrigerant reaches or exceeds its critical pressure. The refrigerant may be a natural refrigerant other than carbon dioxide.

[0029] (1-1) Connecting piping The four connection pipes (2, 3, 4, 5) are composed of a first liquid connection pipe (2), a first gas connection pipe (3), a second liquid connection pipe (4), and a second gas connection pipe (5). The first liquid connection pipe (2) and the first gas connection pipe (3) correspond to the air conditioning unit (60). The second liquid connection pipe (4) and the second gas connection pipe (5) correspond to the cooling unit (70).

[0030] (2) Heat source unit The heat source unit (10) has a heat source circuit (11) and an outdoor fan (12). The heat source circuit (11) has a compression element (20), an outdoor heat exchanger (24), and a gas-liquid separator (25). The heat source circuit (11) has a first outdoor expansion valve (26) and a second outdoor expansion valve (27). The heat source circuit (11) further has a subcooling heat exchanger (28) and an intercooler (29).

[0031] The heat source circuit (11) has four shut-off valves (13, 14, 15, 16). The four shut-off valves are a first gas shut-off valve (13), a first liquid shut-off valve (14), a second gas shut-off valve (15), and a second liquid shut-off valve (16).

[0032] The first gas stop valve (13) is connected to the first gas connection pipe (3). The first liquid stop valve (14) is connected to the first liquid connection pipe (2). The second gas stop valve (15) is connected to the second gas connection pipe (5). The second liquid stop valve (16) is connected to the second liquid connection pipe (4).

[0033] The heat source unit (10) has a flow path switching mechanism (30). In the piping diagram of the refrigerant circuit in Fig. 1 and the like, the details of the flow path switching mechanism (30) are omitted. The flow path switching mechanism (30) switches the flow path of the refrigerant in the refrigerant circuit (6). The details of the flow path switching mechanism (30) will be described later.

[0034] (2-1) Compression element The compression element (20) compresses the refrigerant. The compression element (20) has a first low stage compressor (21), a second low stage compressor (22), and a high stage compressor (23). The compression element (20) performs an operation to compress the refrigerant in a single stage and an operation to compress the refrigerant in two stages.

[0035] The first low-stage compressor (21) is a cold-conditioning compressor corresponding to the cold-conditioning unit (70). The second low-stage compressor (22) is an air-conditioning compressor corresponding to the air-conditioning unit (60). The first low-stage compressor (21) and the second low-stage compressor (22) are an example of a low-stage compression section. The first low-stage compressor (21) and the second low-stage compressor (22) are connected in parallel.

[0036] The high-stage compressor (23) is an example of a high-stage compression section. The high-stage compressor (23) is connected in series to the first low-stage compressor (21) or in series to the second low-stage compressor (22).

[0037] The first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23) are rotary compressors whose compression mechanisms are driven by a motor. The first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23) are variable capacity compressors. The rotation speeds of the motors of the first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23) are adjusted by an inverter device. In other words, the first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23) are configured so that their operating capacities are adjustable.

[0038] A first suction pipe (21a) is connected to the suction side of the first low stage compressor (21). A first discharge pipe (21b) is connected to the discharge side of the first low stage compressor (21). A second suction pipe (22a) is connected to the suction side of the second low stage compressor (22). A second discharge pipe (22b) is connected to the discharge side of the second low stage compressor (22). A third suction pipe (23a) is connected to the suction side of the high stage compressor (23). A third discharge pipe (23b) is connected to the discharge side of the high stage compressor (23).

[0039] (2-2) Intermediate flow path The heat source circuit (11) includes an intermediate flow path (18). The intermediate flow path (18) connects the discharge sides of the first low stage compressor (21) and the second low stage compressor (22) to the suction side of the high stage compressor (23). The intermediate flow path (18) includes a first discharge pipe (21b), a second discharge pipe (22b), and a third suction pipe (23a).

[0040] (2-3) Outdoor heat exchanger and outdoor fan The outdoor heat exchanger (24) is an example of a heat source side heat exchanger. The outdoor heat exchanger (24) is a fin-and-tube type air heat exchanger. The outdoor fan (12) is disposed near the outdoor heat exchanger (24). The outdoor fan (12) transports outdoor air. The outdoor heat exchanger exchanges heat between a refrigerant flowing therethrough and the outdoor air transported by the outdoor fan (12).

[0041] (2-4) Liquid side flow path The heat source circuit (11) includes a liquid side flow path (40). The liquid side flow path (40) is provided between a liquid side end of the outdoor heat exchanger (24) and the two liquid stop valves (14, 16). The liquid side flow path (40) includes first to fifth pipes (40a, 40b, 40c, 40d, 40e).

[0042] One end of the first pipe (40a) is connected to the liquid side end of the outdoor heat exchanger (24). The other end of the first pipe (40a) is connected to the top of the gas-liquid separator (25). One end of the second pipe (40b) is connected to the bottom of the gas-liquid separator (25). The other end of the second pipe (40b) is connected to the second liquid stop valve (16). One end of the third pipe (40c) is connected to a middle portion of the second pipe (40b). The other end of the third pipe (40c) is connected to the first liquid stop valve (14). One end of the fourth pipe (40d) is connected to the first pipe (40a) between the first outdoor expansion valve (26) and the gas-liquid separator (25). The other end of the fourth pipe (40d) is connected to a middle portion of the third pipe (40c). One end of the fifth pipe (40e) is connected to the first pipe (40a) between the outdoor heat exchanger (24) and the first outdoor expansion valve (26). The other end of the fifth pipe (40e) is connected to the second pipe (40b) between the junction of the gas-liquid separator (25) and the third pipe (40c).

[0043] (2-5) Outdoor expansion valve The first outdoor expansion valve (26) is provided in the first pipe (40a). The first outdoor expansion valve (26) is provided in the first pipe (40a) between the liquid side end of the outdoor heat exchanger (24) and the connection portion of the fourth pipe (40d). The second outdoor expansion valve (27) is provided in the fifth pipe (40e). The first outdoor expansion valve (26) and the second outdoor expansion valve (27) are expansion valves whose opening degrees are adjustable. The first outdoor expansion valve (26) and the second outdoor expansion valve (27) are electronic expansion valves whose opening degrees are adjusted based on a pulse signal.

[0044] (2-6) Gas-liquid separator The gas-liquid separator (25) is provided in the liquid-side flow path (40). The liquid-side flow path (40) is a sealed container that stores a refrigerant. The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant. A gas storage section and a liquid storage section are formed inside the gas-liquid separator (25). The gas storage section is formed on the top side of the gas-liquid separator (25). The liquid storage section is formed on the bottom side of the gas-liquid separator (25).

[0045] (2-7) Gas vent pipe The heat source circuit (11) has a gas vent pipe (41). One end of the gas vent pipe (41) is connected to the top of the gas-liquid separator (25). The other end of the gas vent pipe (41) is connected to the intermediate flow path (18). The gas vent pipe (41) sends gas refrigerant in the gas-liquid separator (25) to the intermediate flow path (18). The gas vent pipe (41) is a gas vent flow path that connects the inside of the gas-liquid separator (25) (strictly speaking, a gas storage section) with the suction side of the high-stage compressor (23), which is a high-stage compression section.

[0046] The gas vent pipe (41) is provided with a first valve, that is, a gas vent valve (42). The gas vent valve (42) is an expansion valve whose opening is adjustable. The gas vent valve (42) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

[0047] (2-8) Supercooling heat exchanger The subcooling heat exchanger (28) has a first flow path (28a) which is a high-pressure side flow path and a second flow path (28b) which is a low-pressure side flow path. The subcooling heat exchanger (28) exchanges heat between the refrigerant in the first flow path (28a) and the refrigerant in the second flow path (28b). In other words, the subcooling heat exchanger (28) cools the refrigerant flowing through the first flow path (28a) by the refrigerant flowing through the second flow path (28b).

[0048] The second flow path (28b) constitutes a part of the injection flow path (43). The injection flow path (43) includes an upstream flow path (44) and a downstream flow path (45).

[0049] One end of the upstream flow path (44) is connected to the third pipe (40c) upstream of the connection portion of the fourth pipe (40d). The other end of the upstream flow path (44) is connected to an inlet end of the second flow path (28b). The upstream flow path (44) is provided with an injection valve (46) serving as a subcooling side pressure reducing valve. The injection valve (46) is an expansion valve whose opening is adjustable. The injection valve (46) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

[0050] One end of the downstream flow path (45) is connected to the outlet end of the second flow path (28b), and the other end of the downstream flow path (45) is connected to the intermediate flow path (18).

[0051] (2-9) Intercooler The intercooler (29) is provided in the intermediate flow path (18). The intercooler (29) is a fin-and-tube type air heat exchanger. A cooling fan (29a) is disposed near the intercooler (29). The intercooler (29) exchanges heat between the refrigerant flowing therethrough and the outdoor air transported by the cooling fan (29a).

[0052] (2-10) Oil separation circuit The heat source circuit (11) includes an oil separation circuit. The oil separation circuit has an oil separator (50), a first oil return pipe (51), and a second oil return pipe (52).

[0053] The oil separator (50) is connected to the third discharge pipe (23b). The oil separator (50) separates oil from the refrigerant discharged from the compression element (20). The inflow ends of the first oil return pipe (51) and the second oil return pipe (52) communicate with the oil separator (50). The outflow end of the first oil return pipe (51) is connected to the intermediate flow path (18). The first oil return pipe (51) is provided with a first oil amount control valve (53).

[0054] The outlet side of the second oil return pipe (52) is separated into a first branch pipe (52a) and a second branch pipe (52b). The first branch pipe (52a) is connected to an oil reservoir of the first low-stage compressor (21). The second branch pipe (52b) is connected to an oil reservoir of the second low-stage compressor (22). A second oil amount control valve (54) is provided in the first branch pipe (52a). A third oil amount control valve (55) is provided in the second branch pipe (52b).

[0055] (2-11) Bypass pipe The heat source circuit (11) has a first bypass pipe (56), a second bypass pipe (57), and a third bypass pipe (58). The first bypass pipe (56) corresponds to the first low stage compressor (21). The second bypass pipe (57) corresponds to the second low stage compressor (22). The third bypass pipe (58) corresponds to the high stage compressor (23).

[0056] Specifically, the first bypass pipe (56) directly connects the first suction pipe (21a) to the first discharge pipe (21b). The second bypass pipe (57) directly connects the second suction pipe (22a) to the second discharge pipe (22b). The third bypass pipe (58) directly connects the third suction pipe (23a) to the third discharge pipe (23b).

[0057] (2-12) Check valve The heat source circuit (11) has a plurality of check valves, including first to twelfth check valves (CV1 to CV12). These check valves (CV1 to CV12) allow the refrigerant to flow in the direction of the arrows in Fig. 1 and prohibit the refrigerant from flowing in the opposite direction.

[0058] The first check valve (CV1) and the second check valve (CV2) are provided in a flow path switching mechanism (30), the details of which will be described later.

[0059] The third check valve (CV3) is provided in the third discharge pipe (23b). The fourth check valve (CV4) is provided in the first pipe (40a). The fifth check valve (CV5) is provided in the third pipe (40c). The sixth check valve (CV6) is provided in the fourth pipe (40d). The seventh check valve (CV7) is provided in the fifth pipe (40e). The eighth check valve (CV8) is provided in the first bypass pipe (56). The ninth check valve (CV9) is provided in the second bypass pipe (57). The tenth check valve (CV10) is provided in the third bypass pipe (58). The eleventh check valve (CV11) is provided in the first discharge pipe (21b). The twelfth check valve (CV12) is provided in the second discharge pipe (22b).

[0060] (3) Air conditioning unit The air conditioning unit (60) is an example of a utilization unit installed indoors. The air conditioning unit (60) includes an indoor circuit (61) and an indoor fan (62). A first liquid connection pipe (2) is connected to a liquid side end of the indoor circuit (61). A first gas connection pipe (3) is connected to a gas side end of the indoor circuit (61).

[0061] The indoor circuit (61) has, in order from the liquid side end to the gas side end, an indoor expansion valve (63) and an indoor heat exchanger (64). The indoor expansion valve (63) is an expansion valve whose opening is adjustable. The indoor expansion valve (63) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

[0062] The indoor heat exchanger (64) is a fin-and-tube air heat exchanger. The indoor heat exchanger (64) is an example of a first utilization-side heat exchanger. The indoor fan (62) is disposed near the indoor heat exchanger (64). The indoor fan (62) transports indoor air. The indoor heat exchanger (64) exchanges heat between the refrigerant flowing therethrough and the indoor air transported by the indoor fan (62).

[0063] (4) Refrigeration unit The refrigeration unit (70) is an example of a utilization unit that cools the interior of the refrigerator. The refrigeration unit (70) has a refrigeration circuit (71) and a refrigeration fan (72). A second liquid connection pipe (4) is connected to a liquid side end of the refrigeration circuit (71). A second gas connection pipe (5) is connected to a gas side end of the refrigeration circuit (71).

[0064] The cold-service circuit (71) has, in order from the liquid side end to the gas side end, a cold-service expansion valve (73) and a cold-service heat exchanger (74). The cold-service expansion valve (73) is an expansion valve whose opening is adjustable. The cold-service expansion valve (73) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

[0065] The cold-setting heat exchanger (74) is a fin-and-tube air heat exchanger. The cold-setting heat exchanger (74) is an example of a utilization-side heat exchanger. The cold-setting fan (72) is disposed near the cold-setting heat exchanger (74). The cold-setting fan (72) transports the inside air. The cold-setting heat exchanger (74) exchanges heat between the refrigerant flowing therethrough and the inside air transported by the cold-setting fan (72).

[0066] The evaporation temperature of the cold-air heat exchanger (74) is lower than the evaporation temperature of the indoor heat exchanger (64).

[0067] (5) Flow path switching mechanism The flow path switching mechanism (30) is provided in the heat source circuit (11). The flow path switching mechanism (30) switches the flow path of the refrigerant circuit (6) so as to switch at least between a first refrigeration cycle and a second refrigeration cycle. The first refrigeration cycle is a refrigeration cycle in which the heat source side heat exchanger (24) functions as a radiator and the utilization side heat exchanger (64, 74) functions as an evaporator. The second refrigeration cycle is a refrigeration cycle in which the heat source side heat exchanger (24) functions as an evaporator and the utilization side heat exchanger (64, 74) functions as a radiator.

[0068] 1 and 3, the flow path switching mechanism (30) has a first port (P1), a second port (P2), a third port (P3), a fourth port (P4), a first switching flow path (31), a second switching flow path (32), a third switching flow path (33), and a fourth switching flow path (34). A first opening and closing mechanism (81) is provided in the first switching flow path (31), a second opening and closing mechanism (82) is provided in the second switching flow path (32), a third opening and closing mechanism (83) is provided in the third switching flow path (33), and a fourth opening and closing mechanism (84) is provided in the fourth switching flow path (34).

[0069] (5-1) Port The first port (P1) is connected to the discharge side of the high-stage compressor (23) via a third discharge pipe (23b). The second port (P2) is connected to the suction side of the second low-stage compressor (22) via a suction line (L1). The third port (P3) is connected to the gas end of the indoor heat exchanger (64) via a first gas line (L2). The fourth port (P4) is connected to the gas end of the outdoor heat exchanger (24) via a second gas line (L3). The suction line (L1), the first gas line (L2), and the second gas line (L3) also include piping and component devices connected to the piping.

[0070] (5-2) Flow path As shown in FIG. 1, the first switching flow path (31), the second switching flow path (32), the third switching flow path (33), and the fourth switching flow path (34) are connected in a bridge shape. The first switching flow path (31) connects the first port (P1) and the third port (P3). The second switching flow path (32) connects the first port (P1) and the fourth port (P4). The third switching flow path (33) connects the second port (P2) and the third port (P3). The fourth switching flow path (34) connects the second port (P2) and the fourth port (P4). The first switching flow path (31) and the second switching flow path (32) are high-pressure side flow paths on which a high pressure acts. In other words, the first switching flow path (31) and the second switching flow path (32) are discharge-side flow paths on which the discharge pressure of the compression element (20) acts. The third switching flow path (33) and the fourth switching flow path (34) are low-pressure-side flow paths on which the low pressure acts. The third switching flow path (33) and the fourth switching flow path (34) are suction-side flow paths on which the suction pressure of the compression element (20) acts.

[0071] As shown in FIG. 3, the first switching flow path (31) has two or more first branch paths (31a) that are parallel to one another. The first switching flow path (31) of this example has seven first branch paths (31a). The second switching flow path (32) of this example has two or more second branch paths (32a) that are parallel to one another. The second switching flow path (32) has seven second branch paths (32a). The third switching flow path (33) has two or more third branch paths (33a) that are parallel to one another. The third switching flow path (33) of this example has four third branch paths (33a). The fourth switching flow path (34) is formed of one flow path.

[0072] (5-3) Opening and closing mechanism The first opening / closing mechanism (81) has a plurality of first opening / closing valves (V1). Two or more first opening / closing valves (V1) are provided in parallel in the first switching flow path (31). In this example, seven first opening / closing valves (V1) are provided in the first switching flow path (31). One first opening / closing valve (V1) is provided in each of the first branch flow paths (31a). The plurality of first opening / closing valves (V1) include a first expansion valve (91) and a first solenoid opening / closing valve (92). There is one first expansion valve (91), and six first solenoid opening / closing valves (92). The first expansion valve (91) is an electronic expansion valve whose opening degree is variable.

[0073] The second opening / closing mechanism (82) has a plurality of second opening / closing valves (V2). Two or more second opening / closing valves (V2) are provided in parallel in the second switching flow path (32). In this example, seven second opening / closing valves (V2) are provided in the second switching flow path (32). One second opening / closing valve (V2) is provided in each of the second branch flow paths (32a). The plurality of second opening / closing valves (V2) include a second expansion valve (93) and a second solenoid opening / closing valve (94). The number of the second expansion valve (93) is one, and the number of the second solenoid opening / closing valves (94) is six. The second expansion valve (93) is an electronic expansion valve whose opening degree is variable.

[0074] The third opening / closing mechanism (83) has a plurality of third opening / closing valves (V3). Two or more third opening / closing valves (V3) are provided in parallel in the second switching flow path (32). In this example, four third opening / closing valves (V3) are provided in the third switching flow path (33). Each of the third branch flow paths (33a) is provided with one third opening / closing valve (V3). These third opening / closing valves (V3) are solenoid opening / closing valves.

[0075] The fourth opening / closing mechanism (84) has one fourth opening / closing valve (V4). The fourth switching flow path (34) is provided with the fourth opening / closing valve (V4). The fourth opening / closing valve (V4) is an electromagnetic opening / closing valve.

[0076] The first on-off valve (V1), the second on-off valve (V2), the third on-off valve (V3), and the fourth on-off valve (V4) may be simply referred to as on-off valves (V) as shown in FIG.

[0077] (5-5) Check valve The flow path switching mechanism (30) has check valves (CV1, CV2). Specifically, a first check valve (CV1) is provided in the fourth switching flow path (34). A second check valve (CV2) is provided in the first switching flow path (31).

[0078] The first check valve (CV1) restricts the flow of refrigerant from the second port (P2) to the fourth port (P4) in the switching fourth flow path (34). Strictly speaking, the first check valve (CV1) allows the flow of refrigerant from the fourth port (P4) to the second port (P2) in the switching fourth flow path (34) and prohibits the flow of refrigerant from the second port (P2) to the fourth port (P4). The first check valve (CV1) is provided in the switching fourth flow path (34) closer to the second port (P2) than the on-off valve (V).

[0079] The second check valve (CV2) restricts the flow of refrigerant from the third port (P3) to the first port (P1) in the first switching flow path (31). Strictly speaking, the second check valve (CV2) allows the flow of refrigerant from the first port (P1) to the third port (P3) in the first switching flow path (31) and prohibits the flow of refrigerant from the third port (P3) to the first port (P1). The second check valve (CV2) is provided in the main flow path (31b) in the first switching flow path (31). The main flow path (31b) is a flow path to which the ends of the multiple first branch flow paths (31a) are connected. The second check valve (CV2) is provided in the first switching flow path (31) closer to the third port (P3) than the on-off valve (V).

[0080] (6) Sensors As shown in Fig. 1, the refrigeration system (1) has a plurality of sensors, including a refrigerant pressure sensor that detects the pressure of the refrigerant, a refrigerant temperature sensor that detects the temperature of the refrigerant, and an air temperature sensor that detects the temperature of the air.

[0081] The refrigerant pressure sensors include a high-pressure pressure sensor (101), an intermediate pressure sensor (102), a first suction pressure sensor (103), a second suction pressure sensor (104), and a liquid-side pressure sensor (105). The high-pressure pressure sensor (101) is provided in the third discharge pipe (23b). The high-pressure pressure sensor (101) detects the pressure of the refrigerant on the discharge side of the compression element (20), in other words, the high-pressure pressure of the refrigerant circuit (6). The intermediate pressure sensor (102) is provided in the third suction pipe (23a). The intermediate pressure sensor (102) detects the pressure of the refrigerant between the low-stage compressor and the high-stage compressor, in other words, the intermediate pressure of the refrigerant circuit (6). The first suction pressure sensor (103) is provided in the first suction pipe (21a). The first suction pressure sensor (103) detects the pressure of the refrigerant on the suction side of the first low-stage compressor (21). The second suction pressure sensor (104) is provided in the second suction pipe (22a) and detects the pressure of the refrigerant on the suction side of the second low stage compressor (22).

[0082] The liquid side pressure sensor (105) is provided in the liquid side flow path (40). Specifically, the liquid side pressure sensor (105) is provided in the second pipe (40b). The liquid side pressure sensor (105) detects a pressure corresponding to the internal pressure of the gas-liquid separator (25). The liquid side pressure sensor (105) detects a pressure corresponding to the pressure of the refrigerant in the first flow path (28a).

[0083] The refrigerant temperature sensors include a first discharge temperature sensor (111), a first suction temperature sensor (112), a second discharge temperature sensor (113), a second suction temperature sensor (114), a third discharge temperature sensor (115), a third suction temperature sensor (116), a liquid-side temperature sensor (117), an injection-side temperature sensor (118), and a heat-source-side temperature sensor (119). The first discharge temperature sensor (111) is provided in the first discharge pipe (21b) and detects the temperature of the refrigerant discharged from the first low-stage compressor (21). The first suction temperature sensor (112) is provided in the first suction pipe (21a) and detects the temperature of the refrigerant sucked into the first low-stage compressor (21). The second discharge temperature sensor (113) is provided in the second discharge pipe (22b) and detects the temperature of the refrigerant discharged from the second low-stage compressor (22). The second intake temperature sensor (114) is provided in the second intake pipe (22a) and detects the temperature of the refrigerant sucked into the second low-stage compressor (22). The third discharge temperature sensor (115) is provided in the third discharge pipe (23b) and detects the temperature of the refrigerant discharged from the high-stage compressor (23). The third intake temperature sensor (116) is provided in the third intake pipe (23a) and detects the temperature of the refrigerant sucked into the high-stage compressor (23).

[0084] The liquid side temperature sensor (117) is provided in the liquid side flow path (40). Specifically, the liquid side temperature sensor (117) is provided in the liquid side flow path (40) on the outlet side of the first flow path (28a) of the subcooling heat exchanger (28). More specifically, the liquid side temperature sensor (117) is provided in the liquid side flow path (40) between the outlet end of the first flow path (28a) and the inlet end of the injection flow path (43). The liquid side temperature sensor (117) detects the temperature of the refrigerant that has flowed out of the first flow path (28a).

[0085] The injection side temperature sensor (118) is provided in the downstream flow path (45) of the injection flow path (43). In other words, the injection side temperature sensor (118) is provided on the outlet side of the second flow path (28b) of the subcooling heat exchanger (28). The injection side temperature sensor (118) detects the temperature of the refrigerant that has flowed out of the second flow path (28b).

[0086] The heat source side temperature sensor (119) is provided on a heat transfer tube of the outdoor heat exchanger (24). The heat source side temperature sensor (119) is provided on a liquid side end of the outdoor heat exchanger (24). The heat source side temperature sensor (119) detects the temperature of the refrigerant at the liquid side end of the outdoor heat exchanger (24).

[0087] The air temperature sensor includes an outside air temperature sensor (121) that detects the temperature of the outside air.

[0088] (7) Controller 2, the refrigeration system (1) includes a controller (130) that controls the refrigerant circuit (6). The controller (130) is an example of a control device. The controller (130) includes a microcomputer mounted on a control board and a memory device (specifically, a semiconductor memory) that stores software for operating the microcomputer.

[0089] As shown in Fig. 2, the controller (130) includes an outdoor controller (131), an indoor controller (132), and a cold-conditioning controller (133). As shown in Fig. 1, the outdoor controller (131) is provided in the heat source unit (10). The indoor controller (132) is provided in the air conditioning unit (60). The cold-conditioning controller (133) is provided in the cold-conditioning unit (70). The outdoor controller (131) is capable of communicating with the indoor controller (132) and the cold-conditioning controller (133).

[0090] The controller (130) receives control commands and detection signals from the sensors. The controller (130) controls the devices of the refrigeration system (1). Specifically, the controller (130) controls ON / OFF of the first low stage compressor (21), the second low stage compressor (22), and the high stage compressor (23). The controller (130) adjusts the capacity (strictly speaking, the rotation speed of the motor) of the first low stage compressor (21), the second low stage compressor (22), and the high stage compressor (23). The controller (130) controls ON / OFF of the fans (12, 62, 72). The controller (130) adjusts the opening degree of the expansion valves (26, 27, 63). The controller (130) switches the open / closed state of the valves (42, 43). The controller (130) switches the open / closed state of each on-off valve (V) and adjusts the opening degree of each on-off valve (V).

[0091] (8) Driving behavior The operation of the refrigeration system (1) will be described. The operation of the refrigeration system (1) includes cooling operation, cooling operation, cooling and cooling operation, heating operation, heating and cooling operation, and defrost operation. The heating and cooling operation includes a first heating and cooling operation, a second heating and cooling operation, and a third heating and cooling operation.

[0092] In cooling operation, the cooling unit (70) cools the air inside the cabinet, and the air conditioning unit (60) is stopped. In cooling operation, the cooling unit (70) is stopped, and the air conditioning unit (60) cools the room. In cooling / cooling operation, the cooling unit (70) cools the air inside the cabinet, and the air conditioning unit (60) cools the room. In heating operation, the cooling unit (70) is stopped, and the air conditioning unit (60) heats the room. In heating / cooling operation, the cooling unit (70) cools the air inside the cabinet, and the air conditioning unit (60) heats the room. In defrost operation, frost adhering to the outdoor heat exchanger (24) is melted.

[0093] The first heating / cooling operation is an operation in which the heat absorbed by the refrigerant in the outdoor heat exchanger (24) and the cooling heat exchanger (74) is used for heating. The second heating / cooling operation is an operation in which the outdoor heat exchanger (24) is not functioned and the heat absorbed by the refrigerant in the cooling heat exchanger (74) is used for heating. The third heating / cooling operation is an operation in which the heat of the refrigerant is released from the outdoor heat exchanger (24).

[0094] An overview of each operation will be described with reference to Fig. 4 to Fig. 10. In the figures, the flow of the refrigerant is indicated by dashed arrows, and the flow path through which the refrigerant flows is made thick. In the figures, the heat exchanger functioning as a radiator is hatched, and the heat exchanger functioning as an evaporator is dotted.

[0095] (8-1) Cooling operation In the cooling operation shown in FIG. 4, the controller (130) closes the first on-off valve (V1), the third on-off valve (V3), and the fourth on-off valve (V4), and opens the second on-off valve (V2). The controller (130) stops the second low-stage compressor (22), and operates the first low-stage compressor (21) and the high-stage compressor (23). The controller (130) opens the first outdoor expansion valve (26) and the injection valve (46) to a predetermined opening degree, and closes the second outdoor expansion valve (27). The controller (130) closes the indoor expansion valve (63), and adjusts the opening degree of the cooling-set expansion valve (73). The controller (130) operates the outdoor fan (12) and the cooling-set fan (72), and stops the indoor fan (62).

[0096] In the cooling operation, a refrigeration cycle is performed in which the outdoor heat exchanger (24) functions as a radiator, the indoor heat exchanger (64) substantially stops functioning, and the cooling heat exchanger (74) functions as an evaporator.

[0097] Specifically, the refrigerant compressed by the first low-stage compressor (21) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). The refrigerant compressed to or above its critical pressure by the high-stage compressor (23) dissipates heat in the outdoor heat exchanger (24) and then passes through the first outdoor expansion valve (26). The first outdoor expansion valve (26) reduces the pressure of the refrigerant to a pressure lower than the critical pressure.

[0098] The refrigerant in a subcritical state flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0099] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0100] The refrigerant cooled by the subcooling heat exchanger (28) is sent to the cold storage unit (70). The refrigerant sent to the cold storage unit (70) is reduced in pressure by the cold storage expansion valve (73) and then evaporated in the cold storage heat exchanger (74). As a result, the air inside the storage compartment is cooled. The refrigerant evaporated in the cold storage heat exchanger (74) is sucked into the first low stage compressor (21) and compressed again.

[0101] (8-2) Cooling operation In the cooling operation shown in FIG. 5, the controller (130) closes the first on-off valve (V1) and the fourth on-off valve (V4) and opens the second on-off valve (V2) and the third on-off valve (V3). The controller (130) stops the first low-stage compressor (21) and operates the second low-stage compressor (22) and the high-stage compressor (23). The controller (130) opens the first outdoor expansion valve (26) and the injection valve (46) to a predetermined opening degree and closes the second outdoor expansion valve (27). The controller (130) closes the cold-setting expansion valve (73) and adjusts the opening degree of the indoor expansion valve (63). The controller (130) operates the outdoor fan (12) and the indoor fan (62) and stops the cold-setting fan (72).

[0102] In the cooling operation, a refrigeration cycle is performed in which the outdoor heat exchanger (24) functions as a radiator, the indoor heat exchanger (64) functions as an evaporator, and the function of the cooling-set heat exchanger (74) is substantially stopped.

[0103] Specifically, the refrigerant compressed by the second low-stage compressor (22) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). The refrigerant compressed to or above its critical pressure by the high-stage compressor (23) dissipates heat in the outdoor heat exchanger (24) and then passes through the first outdoor expansion valve (26). The first outdoor expansion valve (26) reduces the pressure of the refrigerant to a pressure lower than the critical pressure.

[0104] The refrigerant in a subcritical state flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0105] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0106] The refrigerant cooled by the subcooling heat exchanger (28) is sent to the air conditioning unit (60). The refrigerant sent to the air conditioning unit (60) is reduced in pressure by the indoor expansion valve (63) and then evaporated in the indoor heat exchanger (64). As a result, the air in the room is cooled. The refrigerant evaporated in the indoor heat exchanger (64) is sucked into the second low stage compressor (22) and compressed again.

[0107] (8-3) Cooling operation In the cooling-use cooling operation shown in FIG. 6, the controller (130) closes the first on-off valve (V1) and the fourth on-off valve (V4) and opens the second on-off valve (V2) and the third on-off valve (V3). The controller (130) operates the first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23). The controller (130) opens the first outdoor expansion valve (26) and the injection valve (46) to a predetermined opening degree and closes the second outdoor expansion valve (27). The controller (130) adjusts the opening degree of the cooling-use expansion valve (73) and the indoor expansion valve (63). The controller (130) operates the outdoor fan (12), the indoor fan (62), and the cooling-use fan (72).

[0108] In the cooling-use cooling operation, a refrigeration cycle is performed in which the outdoor heat exchanger (24) functions as a radiator, and the indoor heat exchanger (64) and the cold-use heat exchanger (74) function as evaporators.

[0109] Specifically, the refrigerant compressed by the first low-stage compressor (21) and the second low-stage compressor (22) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). The refrigerant compressed to or above its critical pressure by the high-stage compressor (23) dissipates heat in the outdoor heat exchanger (24) and then passes through the first outdoor expansion valve (26). The first outdoor expansion valve (26) reduces the pressure of the refrigerant to a pressure lower than the critical pressure.

[0110] The refrigerant in a subcritical state flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0111] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0112] The refrigerant cooled by the subcooling heat exchanger (28) is sent to the air conditioning unit (60) and the cold setting unit (70). The refrigerant sent to the air conditioning unit (60) is reduced in pressure by the indoor expansion valve (63) and then evaporated in the indoor heat exchanger (64). As a result, the air in the room is cooled. The refrigerant evaporated in the indoor heat exchanger (64) is sucked into the first low stage compressor (21) and compressed again.

[0113] The refrigerant sent to the cold-setting unit (70) is decompressed by the cold-setting expansion valve (73) and then evaporated in the cold-setting heat exchanger (74). As a result, the air inside the storage compartment is cooled. The refrigerant evaporated in the cold-setting heat exchanger (74) is sucked into the second low-stage compressor (22) and compressed again.

[0114] (8-4) Heating operation In the heating operation shown in FIG. 7, the controller (130) closes the second on-off valve (V2) and the third on-off valve (V3) and opens the first on-off valve (V1) and the fourth on-off valve (V4). The controller (130) stops the first low-stage compressor (21) and operates the second low-stage compressor (22) and the high-stage compressor (23). The controller (130) opens the second outdoor expansion valve (27) and the injection valve (46) to a predetermined opening degree and closes the first outdoor expansion valve (26). The controller (130) closes the cold-setting expansion valve (73) and adjusts the opening degree of the indoor expansion valve (63). The controller (130) operates the outdoor fan (12) and the indoor fan (62) and stops the cold-setting fan (72).

[0115] In the heating operation, a refrigeration cycle is performed in which the indoor heat exchanger (64) functions as a radiator, the outdoor heat exchanger (24) functions as an evaporator, and the function of the cooling heat exchanger (74) is substantially stopped.

[0116] Specifically, the refrigerant compressed by the second low-stage compressor (22) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). The refrigerant compressed by the high-stage compressor (23) is sent to the air conditioning unit (60).

[0117] The refrigerant sent to the air conditioning unit (60) dissipates heat in the indoor heat exchanger (64). As a result, the air in the room is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (64) flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0118] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0119] The refrigerant cooled by the subcooling heat exchanger (28) is reduced in pressure by the second outdoor expansion valve (27) and then evaporated in the outdoor heat exchanger (24). The refrigerant evaporated in the outdoor heat exchanger (24) is sucked into the second low-stage compressor (22) and compressed again.

[0120] (8-5) First heating / cooling operation The first heating / cooling operation shown in FIG. 8 is performed when the heating load of the air conditioning unit (60) is high. In the first heating / cooling operation, the controller (130) closes the second on-off valve (V2) and the third on-off valve (V3) and opens the first on-off valve (V1) and the fourth on-off valve (V4). The controller (130) operates the first low-stage compressor (21), the second low-stage compressor (22), and the high-stage compressor (23). The controller (130) opens the second outdoor expansion valve (27) and the injection valve (46) to a predetermined opening degree and closes the first outdoor expansion valve (26). The controller (130) adjusts the opening degree of the indoor expansion valve (63) and the cooling-set expansion valve (73). The controller (130) operates the outdoor fan (12), the indoor fan (62), and the cooling-set fan (72).

[0121] In the first heating / cooling operation, a refrigeration cycle is performed in which the indoor heat exchanger (64) functions as a radiator, and the outdoor heat exchanger (24) and the cooling heat exchanger (74) function as evaporators.

[0122] Specifically, the refrigerant compressed by the first low stage compressor (21) and the second low stage compressor (22) is cooled in the intercooler (29) and then sucked into the high stage compressor (23). The refrigerant compressed by the high stage compressor (23) is sent to the air conditioning unit (60).

[0123] The refrigerant sent to the air conditioning unit (60) dissipates heat in the indoor heat exchanger (64). As a result, the air in the room is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (64) flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0124] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0125] A part of the refrigerant cooled by the subcooling heat exchanger (28) is reduced in pressure by the second outdoor expansion valve (27) and then evaporates in the outdoor heat exchanger (24). The refrigerant evaporated in the outdoor heat exchanger (24) is sucked into the first low stage compressor (21) and compressed again.

[0126] The remainder of the refrigerant cooled by the subcooling heat exchanger (28) is sent to the cold storage unit (70). The refrigerant sent to the cold storage unit (70) is reduced in pressure by the cold storage expansion valve (73) and then evaporated in the cold storage heat exchanger (74). As a result, the air inside the storage compartment is cooled. The refrigerant evaporated in the cold storage heat exchanger (74) is sucked into the second low stage compressor (22) and compressed again.

[0127] (8-6) Second heating / cooling operation The second heating / cooling operation shown in FIG. 9 is performed when the heating load of the air conditioning unit (60) is neither excessively high nor low. In the second heating / cooling operation, the controller (130) closes the second on-off valve (V2), the third on-off valve (V3), and the fourth on-off valve (V4), and opens the first on-off valve (V1). The controller (130) operates the first low-stage compressor (21) and the high-stage compressor (23), and stops the second low-stage compressor (22). The controller (130) opens the injection valve (46) at a predetermined opening degree, and closes the first outdoor expansion valve (26) and the second outdoor expansion valve (27). The controller (130) adjusts the opening degrees of the indoor expansion valve (63) and the cooling-set expansion valve (73). The controller (130) stops the outdoor fan (12) and operates the indoor fan (62) and the cooling fan (72).

[0128] In the second heating / cooling operation, a refrigeration cycle is performed in which the indoor heat exchanger (64) functions as a radiator, the outdoor heat exchanger (24) is substantially stopped, and the cooling heat exchanger (74) functions as an evaporator.

[0129] Specifically, the refrigerant compressed by the first low-stage compressor (21) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). The refrigerant compressed by the high-stage compressor (23) is sent to the air conditioning unit (60).

[0130] The refrigerant sent to the air conditioning unit (60) dissipates heat in the indoor heat exchanger (64). As a result, the air in the room is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (64) flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0131] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0132] The refrigerant cooled by the subcooling heat exchanger (28) is reduced in pressure by the cold-type expansion valve (73) and then evaporates in the cold-type heat exchanger (74). As a result, the air inside the storage compartment is cooled. The refrigerant evaporated in the cold-type heat exchanger (74) is sucked into the first low-stage compressor (21) and compressed again.

[0133] (8-7) Third heating / cooling operation The third heating / cooling operation shown in FIG. 10 is performed when the heating load of the air conditioning unit (60) is low. In the second heating / cooling operation, the controller (130) closes the third on-off valve (V3) and the fourth on-off valve (V4) and opens the first on-off valve (V1) and the second on-off valve (V2). The controller (130) operates the first low-stage compressor (21) and the high-stage compressor (23) and stops the second low-stage compressor (22). The controller (130) opens the injection valve (46) and the first outdoor expansion valve (26) to a predetermined opening degree and closes the second outdoor expansion valve (27). The controller (130) adjusts the opening degree of the indoor expansion valve (63) and the cooling-setup expansion valve (73). The controller (130) operates the outdoor fan (12), the indoor fan (62), and the cooling-setup fan (72).

[0134] In the third heating / cooling operation, a refrigeration cycle is performed in which the indoor heat exchanger (64) and the outdoor heat exchanger (24) function as radiators and the cooling heat exchanger (74) functions as an evaporator.

[0135] Specifically, the refrigerant compressed by the first low-stage compressor (21) is cooled in the intercooler (29) and then sucked into the high-stage compressor (23). A part of the refrigerant compressed by the high-stage compressor (23) is sent to the air conditioning unit (60). The refrigerant sent to the air conditioning unit (60) dissipates heat in the indoor heat exchanger (64). As a result, the air in the room is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (64) flows into the gas-liquid separator (25). The remaining part of the refrigerant compressed by the high-stage compressor (23) dissipates heat in the outdoor heat exchanger (24) and then flows into the gas-liquid separator (25). The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant.

[0136] The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection passage (43). The refrigerant in the injection passage (43) is sent to the intermediate passage (18).

[0137] The refrigerant cooled by the subcooling heat exchanger (28) is reduced in pressure by the cold-type expansion valve (73) and then evaporates in the cold-type heat exchanger (74). As a result, the air inside the storage compartment is cooled. The refrigerant evaporated in the cold-type heat exchanger (74) is sucked into the first low-stage compressor (21) and compressed again.

[0138] (8-8) Defrost operation The defrosting operation is performed in winter or the like to melt frost on the outdoor heat exchanger (24). For example, during heating / cooling operation, when a condition indicating that frost has formed on the outdoor heat exchanger (24) is met, the controller (130) performs the defrosting operation. The basic operation of the defrosting operation is the same as that of the cooling operation shown in FIG. 5 and the cooling / cooling operation shown in FIG. 6. In the outdoor heat exchanger (24), the high-pressure refrigerant dissipates heat to the outside, melting the frost on the surface of the outdoor heat exchanger (24).

[0139] (9) Control of compression element startup Control regarding the start-up of the compression element (20) will be described with reference to Fig. 11. In this embodiment, control is performed to stably start up the compression element (20). This control is applicable to any of the above-mentioned operations of the refrigeration system (1). In the following, the above-mentioned cooling operation (see Fig. 5) will be described as an example.

[0140] During cooling operation, the second low stage compressor (22) serving as a low stage compression section and the high stage compressor (23) serving as a high stage compression section are put into operation (step ST11). When the controller (130) receives a command to stop the cooling operation in step ST12, the controller (130) determines in step ST13 whether or not the high pressure in the refrigerant circuit (6) is equal to or lower than a predetermined value. The high pressure in the refrigerant circuit (6) is detected by the high pressure sensor (101).

[0141] When the high pressure of the refrigerant circuit (6) is higher than the predetermined value (NO in step ST13), the controller (130) executes a first operation of step ST14. In the first operation, the controller (130) increases the opening of the gas vent valve (42). In the first operation, the controller (130) may further increase the opening of the open gas vent valve (42), or may increase the opening of the closed gas vent valve (42) (i.e., opening=0) to open it. When the opening of the gas vent valve (42) increases, the internal pressure of the gas-liquid separator (25) communicating with the suction side of the high-stage compressor (23) decreases. As a result, the high-pressure refrigerant on the outdoor heat exchanger (24) side, which functions as a radiator, flows into the gas-liquid separator (25) side, and the high-pressure of the refrigerant circuit (6) decreases.

[0142] When the high pressure of the refrigerant circuit (6) is equal to or lower than the predetermined value (YES in step ST13), the controller (130) stops the second low stage compressor (22) and the high stage compressor (23).

[0143] As described above, in this embodiment, the first action of reducing the high pressure in the refrigerant circuit (6) is performed immediately before the cooling operation is stopped.

[0144] Thereafter, when the controller (130) receives a command to start the cooling operation (YES in step ST16), in step ST17, the controller (130) executes a second operation of starting the high-stage compressor (23). At this time, the high-pressure in the refrigerant circuit (6) is reduced by the first operation, so that the high-pressure can be prevented from becoming excessively high when the high-stage compressor (23) is started. As a result, it is possible to prevent the high-pressure protection switch from operating and the high-stage compressor (23) from failing to start up normally.

[0145] After the second operation, a third operation (bypass operation) is performed. In the third operation, the second low stage compressor (22) remains stopped and the high stage compressor (23) continues to operate. In the third operation, the high stage compressor (23) is in operation, and the first low stage compressor (21) and the second low stage compressor (22) are stopped. The refrigerant circuit (6) performs a refrigeration cycle in which the outdoor heat exchanger (24) functions as a radiator and the indoor heat exchanger (64) functions as an evaporator.

[0146] In the third operation, the second low-stage compressor (22) is stopped, and the refrigerant on the suction side of the second low-stage compressor (22) flows through the second bypass pipe (57) and is sent to the discharge side of the second low-stage compressor (22). As a result, the pressure on the suction side and the pressure on the discharge side of the second low-stage compressor (22) become substantially the same.

[0147] Next, in step ST19, the controller (130) determines whether or not a start-up condition for a low-stage compression section (in this example, the second low-stage compressor (22)) is satisfied. The start-up condition is at least one of the following conditions A to E. The controller (130) determines whether or not the start-up condition is satisfied based on at least one of the conditions A to E.

[0148] Condition A is that the high-pressure in the refrigerant circuit (6) is equal to or less than a predetermined value. If the second low-stage compressor (22) is started when the high-pressure in the refrigerant circuit (6) is greater than the predetermined value, the high-pressure in the refrigerant circuit (6) may become excessively high. When condition A is satisfied, starting the second low-stage compressor (22) can prevent the high-pressure in the refrigerant circuit (6) from becoming excessively high.

[0149] Condition B is that the difference between the suction pressure of the second low-stage compressor (22) and the discharge pressure of the second low-stage compressor (22) is equal to or smaller than a predetermined value. If the pressure difference between the two is large, the load (e.g., the starting torque of the motor) at the time of starting the second low-stage compressor (22) becomes high, and there is a possibility that the second low-stage compressor (22) cannot be started stably. When condition B is satisfied, the second low-stage compressor (22) is started, whereby the second low-stage compressor (22) can be started under a low load. The suction pressure of the second low-stage compressor (22) is detected by the second suction pressure sensor (104), and the discharge pressure of the second low-stage compressor (22) is detected by the intermediate pressure sensor (102).

[0150] Condition C is that the degree of superheat of the refrigerant sucked into the high-stage compressor (23) is greater than a predetermined value. When the degree of superheat of the refrigerant sucked into the high-stage compressor (23) is low, in other words, when the density ratio of the refrigerant sucked into the high-stage compressor (23) is low, the degree of discharge superheat of the high-stage compressor (23) also increases, and the high-stage compressor (23) operates under a high load. When condition C is satisfied, the second low-stage compressor (22) is operated, whereby the density ratio of the refrigerant sucked into the high-stage compressor (23) increases, and the rotation speed of the high-stage compressor (23) can be reduced. As a result, the load on the high-stage compressor (23) can be reduced.

[0151] The degree of superheat of the refrigerant sucked into the high stage compressor (23) is determined based on the refrigerant temperature detected by the third suction temperature sensor (116) and the saturation temperature corresponding to the pressure detected by the intermediate pressure sensor (102).

[0152] The condition D is that the difference between the suction pressure of the high-stage compressor (23) and the discharge pressure of the high-stage compressor (23) is greater than a predetermined value. When the pressure difference between the two, in other words, the high-low pressure difference in the refrigerant circuit (6), is large, the load on the high-stage compressor (23) becomes high. When the condition D is satisfied, the second low-stage compressor (22) is started, thereby performing a two-stage compression refrigeration cycle under a condition where the high-low pressure difference is relatively high. This can improve the COP (coefficient of performance) of the refrigeration system (1). The suction pressure of the high-stage compressor (23) is detected by the intermediate pressure sensor (102), and the discharge pressure of the high-stage compressor (23) is detected by the high-pressure pressure sensor (101).

[0153] The condition E is that the temperature of the refrigerant discharged from the high-stage compressor (23) is higher than a predetermined value. When the condition E is satisfied, the second low-stage compressor (22) is started, whereby the rotation speed of the high-stage compressor (23) can be reduced, and the discharge temperature of the high-stage compressor (23) can be lowered.

[0154] When the above start-up condition is satisfied in step ST19, the controller (130) performs a fourth operation in step ST20 to start up the second low-stage compressor (22).

[0155] The above control can also be applied to other operations. For example, in the cooling operation of Fig. 4, the above control can be adopted at the start-up of the first low stage compressor (21) and the high stage compressor (23). For example, in the cooling operation of Fig. 6, the above control can be adopted at the start-up of the first low stage compressor (21), the second low stage compressor (22), and the high stage compressor (23).

[0156] In the operation in which the first low-stage compressor (21) is started, in step ST19, the controller (130) determines whether or not a start condition for the first low-stage compressor (21) is satisfied. In this case, the controller (130) determines whether or not the above-mentioned conditions A to E are satisfied, with the first low-stage compressor (21) as the low-stage compression section.

[0157] In an operation in which both the first low-stage compressor (21) and the second low-stage compressor (22) are started, in step ST19, the controller (130) determines whether or not start conditions for the first low-stage compressor (21) and the second low-stage compressor (22) are satisfied. In this case, the controller (130) determines whether or not the above-mentioned conditions A to E are satisfied, with the first low-stage compressor (21) and the second low-stage compressor (22) serving as the low-stage compression section.

[0158] In the operation in which the first low-stage compressor (21) is started, in the third operation (bypass operation) of step ST18, the refrigerant on the suction side of the first low-stage compressor (21) is sent to the discharge side of the first low-stage compressor (21) through the first bypass pipe (56) and is sucked into the high-stage compressor (23).

[0159] In the operation in which the first low-stage compressor (21) and the second low-stage compressor (22) are started, in the third operation (bypass operation) of step ST18, the refrigerant on the suction side of the first low-stage compressor (21) is sent to the discharge side of the first low-stage compressor (21) through the first bypass pipe (56) and is sucked into the high-stage compressor (23). At the same time, the refrigerant on the suction side of the second low-stage compressor (22) is sent to the discharge side of the second low-stage compressor (22) through the second bypass pipe (57) and is sucked into the high-stage compressor (23).

[0160] (10) Features (10-1) Issues The refrigeration system (1) performs a refrigeration cycle in which a refrigerant is compressed to or above its critical pressure using carbon dioxide. The high-pressure of the refrigerant circuit (6) using carbon dioxide is extremely high compared to, for example, an HFC-based refrigerant. Therefore, simply starting the high-stage compressor (23) and the low-stage compressors (21, 22) results in an excessively high high-pressure in the refrigerant circuit (6). When the high-pressure becomes excessively high, a high-pressure protection switch is activated or control is performed to protect the compression element (20), so that the compression element (20) cannot be stably started. In particular, under conditions of high outdoor air temperature, the internal pressure of the outdoor heat exchanger (24) becomes high, and this problem becomes more pronounced.

[0161] (10-2) The controller (130) executes a first operation of reducing the high-pressure of the refrigerant circuit (6), a second operation of starting up the high-stage compression section (23) after the first operation, a third operation of sucking the refrigerant into the high-stage compression section (23) through the second bypass pipe (57) after the second operation, and a fourth operation of starting up the low-stage compression sections (21, 22) after the third operation.

[0162] Since the high-pressure in the refrigerant circuit (6) is reduced by the first operation and then the high-stage compressor (23) is started by the second operation, it is possible to prevent the high-pressure from becoming excessively high when the high-stage compressor (23) is started. In the subsequent third operation, the refrigerant on the suction side of the second low-stage compressor (22) is sent to the discharge side of the second low-stage compressor (22) through the second bypass pipe (57) and is sucked into the high-stage compressor (23). Therefore, when the second low-stage compressor (22) is started, the pressure difference between the suction side and the discharge side can be reduced, so that the load on the second low-stage compressor (22) when starting can be reduced, and the second low-stage compressor (22) can be started stably. The same effects can be obtained when the first low-stage compressor (21) is started.

[0163] (10-3) In the first action, the controller (130) increases the opening of the gas vent valve (42). This reduces the internal pressure of the gas-liquid separator (25), and further reduces the high-pressure in the refrigerant circuit (6). Before the start of the high-stage compressor (23), the high-pressure in the refrigerant circuit (6) can be reliably and quickly reduced.

[0164] (10-4) The controller (130) executes the first action before stopping the high stage compressor (23). Therefore, the high pressure in the refrigerant circuit (6) can be reduced by the time a command to start the operation of the high stage compressor (23) is received.

[0165] (10-5) The controller (130) executes the first two operations after the high pressure of the refrigerant circuit (6) becomes equal to or lower than a predetermined value, so that the high stage compressor (23) can be started up under a condition where the high pressure of the refrigerant circuit (6) is low.

[0166] (11) Variations The above embodiment may have the following modified configurations. Differences from the above embodiment will be described below. Note that the following modified configurations will also be described using the above-mentioned cooling operation (see FIG. 5) as an example.

[0167] (11-1) Variation 1 12, in the first modification, when the controller (130) receives a command to stop operation in step ST12, the controller (130) stops the second low stage compressor (22) and the high stage compressor (23) in step ST21. In other words, in step ST21, the controller (130) stops the refrigeration system (1). Next, in step ST22, the controller (130) determines whether the high pressure of the refrigerant circuit (6) is equal to or lower than a predetermined value.

[0168] When the high-pressure in the refrigerant circuit (6) is higher than the predetermined value (NO in step ST22), the controller (130) executes a first operation of step ST23. In the first operation, the controller (130) increases the opening of the gas vent valve (42). This reduces the high-pressure in the refrigerant circuit (6). When the high-pressure in the refrigerant circuit (6) is lower than the predetermined value (YES in step ST22) and the controller (130) receives an operation start command (YES in step ST24), in step ST17, the controller (130) starts the high-stage compressor (23).

[0169] As described above, in the first modification, the first operation of reducing the high pressure in the refrigerant circuit (6) is performed while the operation of the refrigeration system (1) is stopped. Therefore, the high pressure in the refrigerant circuit (6) can be reduced without affecting the operation of the refrigeration system (1).

[0170] (11-2) Variation 2 As shown in Fig. 13, the refrigeration system (1) of the second modification has a cooling section (95) that cools the inside of the gas-liquid separator (25). The cooling section (95) is provided in the heat source unit (10). The cooling section (95) is composed of a cooling heat exchanger that cools the surface and inside of the gas-liquid separator (25), a spray device that sprays a cooling liquid (e.g., water) on the surface of the gas-liquid separator (25), or a Peltier element that cools the surface of the gas-liquid separator. A heat medium (water or refrigerant) for cooling the inside of the gas-liquid separator (25) flows inside the cooling heat exchanger.

[0171] 14, in the second modification, when the second low-stage compressor (22) and the high-stage compressor (23) are stopped in step ST21, the controller (130) executes step ST31. In step ST31, the controller (130) determines whether the suction pressure of the high-stage compressor (23) is equal to or lower than a predetermined value.

[0172] If the suction pressure of the high-stage compressor (23) is higher than the predetermined value (NO in step ST31), in a first operation in step ST32, the controller (130) operates the cooling unit (95). In the first operation, the cooling unit (95) cools the inside of the gas-liquid separator (25) to reduce the suction pressure of the high-stage compressor (23). Specifically, when the refrigerant in the gas-liquid separator (25) is cooled, the temperature of the refrigerant decreases, and the internal pressure of the gas-liquid separator (25) decreases. The gas storage unit of the gas-liquid separator (25) communicates with the suction side of the high-stage compressor (23) via the gas vent passage (41). Therefore, when the internal pressure of the gas-liquid separator (25) decreases, the suction pressure of the high-stage compressor (23) decreases.

[0173] When the suction pressure of the high-stage compressor (23) is lower than a predetermined value (YES in step ST31) and the controller (130) receives an operation start command (YES in step ST24), in step ST17, the controller (130) starts the high-stage compressor (23). At this time, the suction pressure of the high-stage compressor (23) is low, so that the discharge pressure of the high-stage compressor (23), i.e., the high-pressure pressure of the refrigerant circuit (6), can be prevented from becoming excessively high as a result of the start-up of the high-stage compressor (23).

[0174] The gas-liquid separator (25) may be covered with a heat insulating material. By covering the gas-liquid separator (25) with a heat insulating material, heat input from the outside air to the gas-liquid separator (25) can be suppressed. As a result, an increase in the temperature of the refrigerant in the gas-liquid separator (25) can be suppressed, and the cooling effect of the cooling section (95) on the gas-liquid separator (25) can be improved.

[0175] In the second modification, the controller (130) may execute a first operation of cooling the inside of the gas-liquid separator (25) by the cooling section (95) before stopping the high-stage compressor (23).

[0176] In the second modification, the controller (130) may start the high stage compressor (23) when the high pressure becomes lower than a predetermined value, as in the embodiment.

[0177] (11-3) Variation 3 The first operation of the third modification is different from the first operation of the above embodiment. As shown in Fig. 15, in the third modification, the controller (130) increases the rotation speed of the outdoor fan (12) in the first operation of step ST41. This reduces the temperature of the refrigerant in the outdoor heat exchanger (24) and reduces the high-pressure pressure in the refrigerant circuit (6). This makes it possible to prevent the high-pressure pressure from becoming excessively high when the high-stage compressor (23) is started thereafter.

[0178] (11-4) Variation 4 The first operation of the fourth modification is different from the first operation of the above embodiment. As shown in FIG. 16, in the fourth modification, the controller (130) increases the opening of the first oil amount control valve (53) which is the second valve in the first operation of step ST51. In the first operation, the controller (130) may further increase the opening of the first oil amount control valve (53) which is in the open state, or may increase the opening of the first oil amount control valve (53) which is in the closed state (i.e., opening=0) to open it. When the opening of the first oil amount control valve (53) increases, the discharge side and the suction side of the high-stage compressor (23) are pressure-equalized through the first oil return pipe (51) which is a communication passage. This can reduce the high-pressure in the refrigerant circuit (6). This can prevent the high-pressure from becoming excessively high when the high-stage compressor (23) is started up thereafter.

[0179] (12) Other embodiments The above-described embodiment and each of the modified examples may be configured as follows.

[0180] The compression element (20) may have two or more high-stage compressors connected in parallel. In this case, each of the high-stage compressors constitutes a high-stage compression section. The low-stage compression section may be a single low-stage compressor. The compression element (20) may be a single-shaft two-stage compression type compressor having a high-stage compression mechanism, a low-stage compression mechanism, a drive shaft connected to these, and a motor that drives the drive shaft. In this case, the high-stage compression mechanism constitutes the high-stage compression section, and the low-stage compression mechanism constitutes the low-stage compression section.

[0181] The refrigerant circuit (6) does not necessarily have to include the gas-liquid separator (25).

[0182] The flow path switching mechanism (30) may be any mechanism that switches the flow path of the refrigerant so as to switch at least between the first refrigeration cycle and the second refrigeration cycle. The flow path switching mechanism (30) may be, for example, a combination of two three-way valves or two four-way switching valves.

[0183] The controller (130) may execute the first action when the suction pressure of the high-stage compression section (23) is not equal to or lower than a predetermined value.

[0184] The refrigeration system (1) may be configured such that either the air conditioning unit (60) or the cooling unit (70) is omitted.

[0185] The first utilization side heat exchanger (64) may be a heat exchanger that heats or cools water, brine, etc. The first utilization side heat exchanger (64) may be used as a heat source for a water heater.

[0186] Although the embodiment and modifications have been described above, it will be understood that various modifications in form and details are possible without departing from the spirit and scope of the claims. In addition, elements of the above embodiment, modifications, and other embodiments may be appropriately combined or substituted.

[0187] The descriptions "first," "second," "third," etc. mentioned above are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words. [Industrial Applicability]

[0188] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful for heat source units and refrigeration devices. [Explanation of symbols]

[0189] 1 Refrigeration equipment 6 Refrigerant circuit 10 Heat source unit 12 Outdoor fan (fan) 21,22 Low stage compression section 23 High-stage compressor (high-stage compression section) 24 Outdoor heat exchanger (heat source side heat exchanger) 25 Gas-liquid separator 40 Liquid side flow path 41 Gas vent pipe (gas vent passage) 42 Gas vent valve (first valve) 51 First oil return pipe (connecting passage) 53 First oil control valve (second valve) 56,57 Bypass flow path 95 Cooling section 130 Controller

Claims

1. A heat source unit that is applied to a refrigeration system (1) having a refrigerant circuit (6) that performs a refrigeration cycle in which a refrigerant is compressed to a critical pressure or higher, A low-stage compression section (21, 22); a high-stage compression section (23) that compresses the refrigerant compressed in the low-stage compression sections (21, 22); A heat source side heat exchanger (24); a bypass flow path (56, 57) connecting the suction side and the discharge side of the low-stage compression section (21, 22); A control device (130), The control device (130) a first operation of reducing a high pressure in the refrigerant circuit (6) or a suction pressure of the high stage compression section (23); a second operation of starting up the high-stage compression section (23) after the first operation; a third operation of sucking the refrigerant through the bypass flow path (56, 57) into the high-stage compression section (23) after the second operation; After the third operation, a fourth operation of starting up the low-stage compression section (21, 22) is performed. Heat source unit.

2. a liquid side flow path (40) connected to the heat source side heat exchanger (24); a gas-liquid separator (25) provided in the liquid side flow path (40) for separating the refrigerant into a gas refrigerant and a liquid refrigerant; a gas vent passage (41) connecting the interior of the gas-liquid separator (25) with a suction side of the high-stage compression section (23); a cooling section (95) for cooling the refrigerant inside the gas-liquid separator (25), In the first operation, the control device (130) controls the cooling section (95) to cool the gas-liquid separator (25). The heat source unit according to claim 1 .

3. a fan (12) for conveying air passing through the heat source side heat exchanger (24), The control device (130) increases the rotation speed of the fan (12) in the first operation. The heat source unit according to claim 1 .

4. a liquid side flow path (40) connected to the heat source side heat exchanger (24); a gas-liquid separator (25) provided in the liquid side flow path (40) for separating the refrigerant into a gas refrigerant and a liquid refrigerant; a gas vent passage (41) connecting the interior of the gas-liquid separator (25) with a suction side of the high-stage compression section (23); a first valve (42) provided in the gas vent passage (41), In the first action, the control device (130) increases the opening degree of the first valve (42). The heat source unit according to claim 1 .

5. a communication passage (51) that communicates the discharge side and the suction side of the high-stage compression section (23); a second valve (53) provided in the communication passage (51), In the first action, the control device (130) increases the opening degree of the second valve (53). The heat source unit according to claim 1 .

6. The control device (130) executes the first operation before the high-stage compression section (23) is stopped or while the high-stage compression section (23) is stopped. The heat source unit according to any one of claims 1 to 5.

7. The control device (130) executes the second operation after the high pressure of the refrigerant circuit (6) or the suction pressure of the high-stage compression section (23) becomes equal to or lower than a predetermined value. The heat source unit according to any one of claims 1 to 5.

8. A refrigeration system comprising the heat source unit (10) according to any one of claims 1 to 5.

9. The refrigerant is carbon dioxide.

9. The refrigeration system of claim 8.

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